Air preheater for pulverizing mills



R. s. COOPER ET AL ,41 37 AIR PREHEATER FOR PULVERIZING MILLS FiledApril 21, 1944 2 Shees-Sheet 1 051 mere-1? INVENTORS 50m 1/0/11 y RolandS. foo Mr HTTORNEY M 29, 1946. R. s. COOPER ET AL I 2,410,337

AIR PREHEATER FOR PULVERIZING MILLS Filed April 21, 1944 2 Sheets-Sheet2 Patented Oct. 29, 1946 '4 I OFF "smear I v f AIR rREHEA'rER-FonPULVERIZING' MILLS I Roland S. 'CoopenfRiver Forest, 1 11., and Sven"Holm, Wellsville, N. Y., assignorstofThe Air 7 Preheater' Corporation,NewYork, Y. i 1 Original application ctpber'22,1942,.SerialNo.

462,942. Divided and thistiapplication April 21, .194 Serial No. 532,124

2 Claims. (Cl. 263- 19) The present invention relates to heat exchangewaste gases from a-boiler are passed through 1 an air preheater topreheat the secondary air for combustion of pulverized fuel in theboiler furnace and also to supply primary air to a fuel pulverizing millfor drying the coal therein. However, with coals of high moisturecontent mined in certain parts of the country the proper drying ofpulverized coal requires primary air that has been preheated to a highertemperature than that available or desired for the secondary air usedfor the combustion of the fuel. In accordance with the present inventionair that has been preheated in a conventional air preheater to themaximum temperature obtainable by transfer of heat from waste gases isfurther heated by being passed through a separately fired auxiliaryheater before reaching the pulverizing mill.

The invention will be best understood upon consideration of thefollowing detailed description of an illustrative embodiment thereofwhen read in conjunction with the accompanying drawings in which:

Figure l is a schematic view of an air preheating system supplyingsecondary air to a boiler furnace for the combustion of fuel therein andsupplying primary air for drying the pulverized fuel burn-ed in thefurnace in accordance with the present invention.

Figure 2 is a longitudinal sectional view of the separately firedauxiliary air heater illustrated in Fig. 1;

Figure 3 is a sectional view on the line 3-3 in Fig. 2;

Figure 4 shows an air heater like that in Fig. 2 arranged forrecirculation of the gases of combustion therefrom; and

Figure 5 illustrates a modified form of the air heater shown in Fig. 4.

Referring first to Figure 1, waste gases as from a boiler l0 passthrough the gas side of a Ljungstrom preheater 12 on their way from theboiler ofitake M to the flue I5. Air supplied by a fan, not shown,entering the inlet duct is traverses the air side of the preheater l2and from its outlet l8 flows via a duct 2!] to the furnace of the boilerH] where the preheated air is utilized in the combustion of the fuel.Part of the pr heated air flows from the air preheater l2 by way of abranch duct 22-24 to a coal drying and pulverizing mill 26 from which astream of pulverized coal and primary air isdirected to, the fuel burn-.ers,.byz-a.duct 28.

As mentioned, because the amount of available heat that may betransferredfrom the waste heat gases in boiler offtake duct I4. is

oftentimes not reat enoughto'heat the air flowing through preheater 12'into the air outlet duct 20 to a temperature sufficiently high forproperly drying coal of high moisture content; therefore a separatelyfired auxiliary air heater 30 is interposed in the ducts 22-24 betweenthe air outlet of the preheater l2 and the inlet to the coal drying andpulverizing mill 26. The separately fired air heater shown in Fig. 2consists of a generally cylindrical furnace 30 having a number of liquidor gaseous fuel burners 3| arranged in a circle and projecting throughone end wall 32. Chamber 3!] tapers at its other end for connection tothe duct 24. The duct 22 through which preheated air is taken from themain air preheater I2 is connected to a tube 33 projecting through theend wall 32 and extending axially of the furnace 30 to a point adjacentbut short of its outlet opening 34 which is screened by a 1 fire check35. The burners 3| for injecting the fuel into the furnace 30 arearranged in a circle about tube 33 and set at-an angle with respect tothe longitudinal axis of chamber 3'0 so as to give a tangential firingeffect as is shown in Fig. 3. As the preheated airfrom duct 22 entersthe tube 33 the portion of the air necessary for combustion of fuelflows into the annular furnace space 36 about the tube 33 through anumber of holes 31 in the wall of the latter. These holes are arrangedat such an angle that the air enters the furnace chamber 36 tangentiallyand in opposite direction to the jets of fuel from the burners 3!. Thisresults in good mixing of the fuel with the air discharged from openings31. The portion of the air not used for combustion is discharged fromthe end of the air tube 33 and heated by mixing with the products ofcombustion in a chamber 38 beyond the end of tube 33. I

With the arrangement described, there is good utilization of thecombustion space because the annular combustion chamber formed betweenthe inner wall of the cylindrical furnace 30 and the tapering outsidesurface of tube 33 enlarges from the point of fuel injection toward theoutlet of the furnace thereby increasing the volume of the dischargingthem back into the center tube 43 of t v a plane transverse thereof; anair tube projectthe latter through a duct 44. The secondary air requiredfor combustion of the fuel in this arrangement is introduced at 45around the burners 46. In another form as shown in Fig. 5 the re- 7circulated gases are introduced into the center tube 53 through a pipe54 which is of smaller diameter so that a space 55 is formed around thepipe 54 to which the required secondary air may October'22, 1942, underSerial No. 462,942.

' We claim: 1. A furnace for heating gaseous fluids comprising; meansforming an elongated cylindrical 4 furnace chamber closed at one end; agas discharge duct connected centrally into the opposite end of saidchamber; burners disposed for introducing fuel to be burned to saidchamber through its wall near said one end and arranged in a circle todirect the fuel streams toward and tangentially to an imaginary circlecentered on the longitudinal axis of said chamber and located in ingthrough said one end wall within said burner circle and having an openend located at a point short of the opposite end wall, said tube beingof smaller diameter than the cross sectional area of said chamber toprovide an annular combustion space and being formed in its side wallwith orifices inclined with respect to the axis of said chamber so as todirect air into said annular combustion space in directions opposite tothose of the streams of fuel from said burners.

2. A furnace construction as recited in Claim 1 wherein exterior wall ofsaid air tube tapers to ward said outlet duct so that said annularcombustion space surrounding it increases in volume in the direction ofgas flow.

V v ROLAND s. COOPER.

SVEN HOLM,

